Prior to setting forth a short discussion of the related art, it may be helpful to set forth definitions of certain terms that will be used hereinafter. Many of these terms are defined in the Institute of Electrical and Electronics Engineers (IEEE) 802.11 specification but it should be appreciated that the invention is not limited to systems and methods complying with the IEEE 802.11 specification.
The term “Wi-Fi” is used to refer to technology that allows communication devices to interact wirelessly. The wireless communication may use microwaves, e.g. in the 2.4 GHz and 5 GHz wavebands.
The term “AP” is an acronym for Access Point and is used herein to define a wireless fidelity “Wi-Fi” or other wireless station that is an attachment point for user equipment “UE” to a wireless communications network.
The term “UE” is an acronym for User Equipment(s) and is an example of a station, e.g. Wi-Fi station (STA) that may attach to an AP.
The term “station” or STA is a term used for any participant on the network, for example as used in the 802.11 specification. Both UEs and APs are considered in this context to be examples of stations. In the following the abbreviation STA is used for stations whose packets are detected by a Wi-Fi RDN station implementing embodiments of the invention.
The specific Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) mechanism used in the 802.11 Media Access Control (MAC) is referred to as the distributed coordination function (DCF). A station that wishes to transmit first performs a clear channel assessment (CCA) by sensing the medium for a fixed duration, the DCF inter-frame space (DIFS).
SIFS, Short Inter Frame Space, as defined in the 802.11 specifications is period between reception of the data frame and transmission of the ACK. SIFS is shorter than DIFS.
The term Clear Channel Assessment (CCA) as used herein refers to the CCA function as defined in the 802.11 specifications.
The term Base Band Processor (BBP) as used herein refers to encoding data and decoding data so as to create the required Wi-Fi baseband signal for all versions of the 802.11 protocol(s).
The term Enhanced distributed channel access (EDCA) is an extension of the basic DCF introduced in the 802.11e amendment to support prioritized quality of service (QoS). The EDCA mechanism defines four access categories (ACs).
The term AC is an acronym for Access Category as used herein refers to AC as defined in the 802.11 specifications. Each AC has a specific values of access parameters, e.g., contention window maximum or minimum CWmin or CWmax, Arbitration Inter-Frame Space Number AIFSN and TXOP (transmit opportunity) limit.
The term CW is an acronym for contention window as defined in the 802.11 specifications. The random backoff count (number of slots needed to wait before retransmission) is selected from the range [0, CW], where CW is typically equal to CWmin.
The term transmit opportunity (TXOP) is a bounded period during which a station may transfer data of particular traffic as defined in the 802.11 specifications.
The term power-save multi-poll (PSMP) is a scheduling technique introduced in 802.11n to optimize channel access for devices that receive and transmit small amounts of data periodically and would like their communications interface to remain inactive most of the time to conserve power, i.e. when they are not actively transmitting or receiving frames.
The term “MIMO” is an acronym for multiple input multiple output and as used herein, is defined as the use of multiple antennas at both the transmitter and receiver to improve communication performance. MIMO offers significant increases in data throughput and link range without additional bandwidth or increased transmit power. It achieves this goal by spreading the transmit power over the antennas to achieve spatial multiplexing that improves the spectral efficiency (more bits per second per Hz of bandwidth) or to achieve a diversity gain that improves the link reliability (reduced fading), or increased antenna directivity.
“Channel estimation” is used herein to refer to estimation of channel state information which describes properties of a communication link such as signal to noise ratio “SNR” and signal to interference plus noise ratio “SINR”. Channel estimation may be performed by user equipment or APs as well as other components operating in a communications system.
The term “beamforming” sometimes referred to as “spatial filtering” as used herein, is a signal processing technique used in antenna arrays for directional signal transmission or reception. This is achieved by combining elements in the array in such a way that signals at particular angles experience constructive interference while others experience destructive interference. Beamforming can be used at both the transmitting and receiving ends in order to achieve spatial selectivity.
The term “beamformer” as used herein refers to RF circuitry that implements beamforming and usually includes a combiner and may further include switches, controllable phase shifters, and in some cases amplifiers. At least one of the combiners has antenna distinguishing circuitry, wherein the antenna distinguishing circuitry is configured to distinguish between any one of the signals feeding the combiner. The beamformer is controlled by a processor, e.g. part of UE baseband resources, which uses metrics, e.g. channel estimation of each antenna (also known as a “Look-Thru” process), to calculate and set up beamformer weights, or uses a weights search procedure by tuning one antenna of the beamformer based on SINR or data rate (e.g. using a search algorithm). The weights determine the relative amounts of signals from each antenna that are used in the combiner.
The term “Receiving Radio Distribution Network” or “Rx RDN” or simply “RDN” as used herein is defined as a group of beamformers as set forth above.
A Wi-Fi RDN station equipped with one receive antenna or more may be augmented by replacing the connection between a given receiver input and its antenna with a Radio-Distribution-Network (RDN) that combines several additional antennas together and feeds the RF combined signal to the radio input in such a way that increases directivity and equivalent antenna gain for one or all of the legacy radios in the station.
A Wi-Fi RDN station performs from time to time a look through process (Look-Thru) to obtain channel estimation of a single antenna using antenna distinguishing circuitry configured to selectively disconnect and terminate all but one of the antennas so that only one signal coming from the antennas is conveyed to the combiner's output, at a time; such a Look-Thru can be performed every few packets.